Power transmission belt with tubular knit overcord

ABSTRACT

A power transmission belt is disclosed in which the exterior of the overcord section is generally flat in contour and bears an outer seamless tubular knit textile material adhered to an adjacent rubber layer material interposed between the exterior belt back surface and a strain-resisting tensile section. The belt is adapted to be run against backside idlers or tensioners with minimized noise generation. A simplified process including use of a tubular knit stretched over and applied to the building drum is disclosed, thereby eliminating conventional calendaring and Bannering operations.

[0001] This nonprovisional application claims the benefit of U.S.Provisional Application Nos. 60/165,381 filed Nov. 12, 1999 and60/206,102 filed May 20, 2000.

BACKGROUND OF THE INVENTION

[0002] This invention relates to power transmission belts of the rubbertype, particularly a belt whose back surface is adapted to make contactwith an idler pulley, tensioner or other device tending to generatenoise at the interface of such device with the belt.

[0003] Modern front end accessory drive systems for automobiles useserpentine multi-V-ribbed belts to link the engine crankshaft withvarious accessory driven pulleys. The backside of the belt typicallyimpinges against backside idler pulleys and/or tensioning devices.Similarly, camshaft belt drive systems for automotive applicationsystems use synchronous power transmission belts, the backsides of whichare also trained about idler pulleys and/or tensioners. In addition, inmany industrial belt drive applications, the drives include idlers orother devices against which the back of a multi-V-ribbed belt,synchronous belt, flat belt, V-belt or the like engages. In all of theforegoing automotive and industrial applications, chirping or “thumping”noise may be generated at the interface of the backside of the belt anddrive device. The noise levels are often times unacceptable to themanufacturer or user.

[0004] For instance, overcords of belts of the multi-V-ribbed typetypically employ a crosscord, or a bias laid fabric in which warp andweft yarns are oriented diagonally in respect to the longitudinalrunning direction of the belt, with an included angle between the yarnsof about 90-120 degrees. These textile overcord reinforcements providelateral stability, assist release of the belt slab from its mandrelduring the manufacturing process, and allow tailoring the coefficient offriction on the backside of the belt. Typically these belts' overcordtextile materials are calendared with gum rubber into the interstices(and on the faces) of the fabric and then the frictioned fabric/gumassembly is cut and respliced (using a Banner table-trademark) toprovide the correct fabric cord orientation. This fabric cordorientation provides maximum or optimal lateral strength while allowinghigh flexibility in the longitudinal direction of the belt.

[0005] To effectively use these types of textile composite materials inthe belt overcord, most manufacturing processes require makingoverlapping splices to reconnect the material after “Bannering”, as wellas during the belt building process. These overlap splice joints createdouble thickness areas which have been found to cause noise andvibration in automotive serpentine drives. As the belt rotates aroundthe drive, these splices contact the backside idlers, tensioners and thelike which can cause the belt to chirp and the belt and drive componentsto vibrate.

[0006] With synchronous belt products it is common practice to usetextile jackets which are made of stretch type fabrics, which aretreated for adhesion, cut to length to match a particular belt length,and sewn or ultrasonically stitched back together to form a cylindricaltube or jacket for application to the belt teeth as a facing, or in theovercord. The resulting seams can serve as noise generators, and theoverall process is time consuming and expensive.

[0007] The foregoing belt types also typically bear on their exteriorbelt back surface a label to identify the belt. A typical labelingprocess involves applying a polymeric film e.g. Mylar (Du Ponttrademark) polyester, or other substrate transfer label against the beltsleeve in the course of its vulcanization. The Mylar label embeds intothe outer rubber surface of the belt, and then the Mylar backing isstripped from the sleeve after conclusion of vulcanization, leaving anegative imprint, i.e. ridges or steps in the belt back surface whichserve as additional noise generator sites.

[0008] The use of knit overcord fabrics, per se, is known from U.S. Pat.No. 3,981,206 (Miranti et al). However, in the belt construction ofMiranti et al, the belt is built up on a cylindrical drum by applyingvarious layers of material wrapped therearound, including the outer(nontubular) knit fabric. Such wrapping process will produce a seam orlapped joint, which will serve as a noise generator in backside idlerand tensioner drives.

[0009] Seamless knitted tubular fabrics have also been used in theovercord of power transmission belts of the liquid cast (polyurethane)type. Unexamined Japanese patent application no. 7-243 483(Bridgestone), published Sep. 19, 1995, discloses a multi-V-ribbed beltin which the tubular knit in the overcord is positioned directly againstthe tensile cord prior to liquid casting. The tensile cord and tubularknit make direct contact in the final fabricated liquid cast belt.

[0010] It is an object of this invention to overcome drawbacks in theprior art by providing a rubber power transmission belt utilizing atextile-reinforced overcord section which imparts lateral stability tothe belt while allowing high flexibility in the running direction of thebelt, and is characterized by an overcord free of joints, lapped splicesor seams which would generate noise in belt drives using backsideidlers, tensioners or the like.

[0011] It is a further object to achieve the foregoing without the needto Banner, calendar or otherwise prepare the outside jacket for theovercord of the belt, thus eliminating process steps and cost.

SUMMARY OF THE INVENTION

[0012] These and other objects of the invention are met by a powertransmission belt which includes a rubber body, a strain-resistingtensile member embedded in the body, an overcord section terminating ina generally flat exterior belt back surface, and an undercord section,in which a seamless tubular radially stretchable textile material,preferably a seamless tubular knit textile material, is positioned atthe exterior back belt surface, and a rubber layer is adhered to thetubular knit textile material on its undersurface and is interposedbetween the tubular knit textile material and the strain-resistingmember.

[0013] In another aspect, the power transmission belt of the inventionis manufactured by a method including the steps of applying a seamlesstubular radially stretchable, preferably knit, textile material aboutthe exterior surface of a belt building drum, wrapping a rubber layerserving as an adhesion gum layer over the seamless tubular textilematerial, helically winding strain-resisting tensile cord members aboutthe rubber layer, applying a further rubber layer over the exterior ofthe helically wound tensile cord, and subjecting the belt sleevecomprised of the tubular textile material, first rubber layer,strain-resisting textile cord helically wound about the first rubberlayer, and second rubber layer, to heat and pressure to form avulcanized belt sleeve from which individual belts can be severed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Preferred aspects of this invention will be described withreference to the accompanying drawings, in which like numerals designatelike parts in the several figures, and wherein:

[0015]FIG. 1 is a simplified engine accessory drive system;

[0016]FIG. 2 is a transverse cross section of a multi-V-ribbed belt usedin the accessory drive system of FIG. 1 taken along 2-2;

[0017]FIG. 3 is a partial plan view of a ribbed knit fabric usable inthe overcord section of the belt of the invention;

[0018]FIG. 4 is a plan view of the technical face of a jersey knitconstruction usable in the belt of the invention;

[0019]FIG. 5 is a front view schematic of a synchronous (timing) beltdrive system of the automotive type which includes a tensioner and abackside idler pulley impressed against the backside of the belt of theinvention;

[0020]FIG. 6 is an expanded side elevational view of a synchronous beltused in the belt drive system of FIG. 5;

[0021]FIG. 7 depicts a partial cut-away of a belt building drum(mandrel) showing the different layered components assembled on the drumto construct a belt sleeve in accordance with the invention;

[0022]FIG. 8 illustrates a seamless tubular knit textile material of theinvention in its rest position, as well as partially expanded as shownin phantom;

[0023]FIG. 9 is a partial sectional view of the overcord section of thebelt of FIG. 6 of the invention at 9-9;

[0024]FIG. 10 shows a multi-V-ribbed belt in partial section andperspective with a label applied to its exterior back surface; and

[0025]FIG. 11 is a view similar to FIG. 10 illustrating a prior art beltwith a label applied to its exterior back surface.

DESCRIPTION OF PREFERRED EMBODIMENT

[0026] Referring first to FIGS. 1 and 2 of the drawings, an engineaccessory drive system is shown generally at 10, consisting of an enginecrankshaft 14 pulley, and a driven pulley 12 linked in drivingrelationship by a four-ribbed serpentine belt 11. The top or exteriorback surface of 13 of belt 11 makes contact with idler pulley 16. Thedrive system 10 of FIG. 1 may be used as a simple automotive accessorydrive system, an industrial drive, or a test apparatus for measuringnoise generated at the interface between belt 11 and backside idlerpulley 16 through sensor/transducer 18 (measuring dB's and noisecharacteristics). The particular application and type of drive systemwill be dictated by the type of belt configuration chosen. Generally theprinciples of the invention may be applied to V-belts, flat belts,multi-V-ribbed belts and synchronous belts. An example of a commonautomotive front end accessory drive system in which the belt of theinvention may be used is illustrated and disclosed in U.S. Pat. No.4,551,120, which consists of a main driving pulley operatively connectedto an air conditioning motor pulley, an alternator pulley, an engine airpump pulley, and a water pump pulley. The multi-V-ribbed belt trainedabout these pulleys is kept in appropriate tension through a tensionerhaving a surface engaging the backside of the belt.

[0027] The belt of FIG. 2 is formed of a rubber body. By “rubber” ismeant a cross-linkable natural or synthetic rubber which is processablein solid form, e.g. on a mixing mill. Such rubber is typically mixed ina green or unvulcanized form with appropriate additives, extenders,reinforcements, accelerators, fillers, vulcanizing agents, e.g. sulfurand peroxides, and the like in a Banbury® mixer, or continuous mixer,well known in the rubber processing industry. Layers or calendaredsheets of stock are then ready to be built up in layered form withtextile reinforcement and the like, the green reinforced rubber insleeve or other form is vulcanized or cured under heat and pressure. Ifcured in sleeve form, individual belts may be cut from the sleeve.Typical synthetic rubbers useful in the invention includepolychloroprene, copolymers of ethylene and propylene, terpolymers ofethylene, propylene and diene monomers, e.g. EPDM, styrene butadienerubber, HNBR, CSM, silicone rubber, fluoroelastomers, mixtures of theforegoing, and alloys or mixtures of the foregoing or other knownsolid-processable rubbers mixed with suitable thermoplastic orthermosetting polymers or “plastomers”, polyethylene, polyester (Hytreltrademark) or materials such as Santoprene (Monsanto trademark). Liquidprocessable elastomeric materials such as those formed by liquidcasting, applicable to many forms of polyurethane, are not within thisdefinition and are not contemplated by the invention.

[0028] The belt of FIG. 2 is a four-ribbed serpentine belt employing astrain-resisting tensile member 20 which is embedded in the rubber bodyof the belt. It is positioned by helically winding it as will bediscussed further in respect to the building process described withreference to FIG. 7. The tensile cord members may be any typicalstrain-resisting cord or members formed of Nylon, polyester, carbon,aramid e.g. KEVLAR®, or TWARON® fibers (both trademarks) and the like,and are typically formed of twisted yarns. The yarns, in turn, areusually composed of many fibers. The cords may be sized or treated e.g.with RFL (resorcinol formaldehyde latex), to enhance adhesion to therubber. The undercord or compression section 22 of the belt may beformed of an unloaded rubber stock, however typically it is formed of asuitable rubber in which has been mixed loading of discretereinforcement fibers 24 of desired material such as cotton, polyester oraramid. The multiple ribs of the undercord section shown at 23, 25, 27,29 may be formed by grinding away the fiber loaded rubber betweenadjacent ribs, up to the apex 26 between adjacent ribs, or by molding,fly cutting or other technique. The shape and configuration of the ribsis normally substantially matched to the corresponding shape of thepulleys 12 and 14 about which the belt is linked in drivingrelationship.

[0029] The overcord section of the belt shown at 28 includes a generallyflat exterior belt back surface 13, a seamless tubular radiallystretchable, preferably knit, textile overcord material 15 positioned atthe exterior belt back surface, and an interposed rubber layer such asadhesion gum layer 17 which is selected to adhere to the tubular knittextile material 15 as well as the adjoining cords 20. The adhesion gumlayer 17 may be formed of the same or similar (compatible) rubbermaterial as utilized in the undercord section 22 to ensure properadhesion and integration into the composite belt structure.

[0030] The radially stretchable, preferably knit material 15 is in theform of a seamless tube, such as shown at 30 in FIG. 8 of a restdiameter of D₁ which, because of inherent stretchability of up to 500%or more typically, may be expanded (at 30′) to an increased diameter D₂as shown in phantom. The normal diameter D₁ should be chosen to be equalto or preferably somewhat less than the diameter of the building drum ormandrel, with the rest diameter D₁ of the tubular knit textile materialbeing preferably from about 20 to 100 and more preferably from about 30to about 80 percent of the final diameter of the knit tube as applied instretched condition on the building drum, shown at 31 in FIG. 7. Ingeneral, the degree of expansion, and the corresponding opening size ofinterstices 33, 34 (FIGS. 3 and 4) of the tubular knit material, and itsconstruction (e.g. denier, fiber type and twist, and density of coursesand wales) can be selected to obtain a resultant belt surface with acoefficient of friction selected for optimal belt performance for theapplication.

[0031] Knit tube 30 (FIG. 8) is produced in a seamless tube form, i.e.the circular knitting process inherently produces a tube of a particulardiameter D₁ depending on the preselected equipment components utilizedin the knitting machine. The individual yarns may be formed ofmonofilaments or multiple filaments but typically are formed of bundlesof twisted staple fibers of any suitable material such as cotton,polyester, Nylon, aramid, carbon or mixtures thereof. Alternatively, theyarns may be comprised of individual elastic core filaments covered witha staple or texturized textile sheath. The yarns may be sized or coatedfor enhanced adhesion e.g. with RFL or a compatible rubber dissolved inan organic solvent. It is contemplated that tubes 30 of a given diametermay be useful for more than one belt size given the significantstretchability of the knit tube itself. Different knit patterns may beemployed, such as the rib-knit configuration shown in FIG. 3 in whichthe wales or vertical rows 35 of stitches of yarns 39 intermeshalternately on the face and the back of the knit. Rib-knit fabrics ofthis type have good elasticity, especially in the width direction. Ajersey knit as shown in FIG. 4, formed of a circular knit fabric madewith a plain stitch is currently the most preferred knit fabric for usewith the invention. It is preferred that the technical face, as shown inFIG. 4, faces inwardly (toward the adhesion gum layer 17.) As with therib-knit of FIG. 3, the wales or rows extend vertically in the figures,as well as vertically in the tube of FIG. 8. Such orientation, whenapplied to the belts of FIG. 2 and FIG. 6, for instance, will cause thewales or vertical rows of stitches to be oriented transversely to thelongitudinal (running) direction of the completed belt. Other knit orradially stretchable configurations which can be formed into a seamlesstubular configuration with openings (interstices) allowing rubber flowthrough are also contemplated.

[0032] In the completed belt, the interstices 33, 34 of the knit fabricwill be largely filled with rubber material supplied by the adhesion gumlayer 17. In the most preferred form as shown schematically in FIG. 9,rubber from adhesion gum layer 17 will fill the bulk of the interstices34 of the seamless tubular knit textile material, but the yarns tips 36,38, 40 which form the outermost exterior surface 13 of the top of thebelt, and the fibers of the yarns which are positioned at such belt backsurface, will be free from full encapsulation by the rubber of therubber body. That is, yarn tips 36, 38, 40 and associated fibers will beunencapsulated and present at the generally flat exterior belt backsurface textile fibers for engagement, along with the exposed rubberlayer within the knit interstices, with a tensioner, backside pulley orthe like. Where an increased belt backside coefficient of friction isneeded to prevent slippage with an associated driven pulley or the like,it is preferred to increase the interstice opening 34 (e.g. byincreasing the ratio D₂:D₁).

[0033] Alternatively, although less preferred, as long as the tubularknit textile material is in a seamless, cylindrical form, and adhesionrubber layer 17 is interposed between the tensile cord 20 and the backsurface of the belt, an outermost rubber layer (not shown) may fullyencapsulate the knit fabric and embed the same in rubber and stillbenefit from low noise generation and other advantages of the invention.In this embodiment an extra layer of rubber may be interposed betweenthe building drum 31 and knit tube 30, preferably butt spliced to avoidan overlap splice.

[0034] In FIGS. 5 and 6, a synchronous or “timing” belt drive system 42is shown and includes a toothed or synchronous belt 43 trained andtensioned around a crank pulley 44, an idler pulley 16, and a water pumppulley 46, camshaft pulleys 45, 47 and a tensioner or tensioning pulley48. The tensioner may be of various types including the torsion springarm type disclosed in U.S. Pat. No. 5,938,552 to Serkh.

[0035] Referring to FIG. 6, belt 43 is formed of a rubber body 49 inwhich is embedded a strain-resistant tensile cord 20. A series of cogsor teeth 50 are disposed on the underside of the belt adapted to meshwith the sprocket teeth of camshaft sprockets 45, 47, crankshaft 44 andwater pump pulley 46, in gear-like fashion to transmit power insynchronization. Belt 43, similarly to multi-V-ribbed belt 11 discussedin respect to FIG. 2, employs a seamless tubular knit textile material15 at the exterior back surface 13 of the belt. A layer 17 of rubber ofadhesion gum type is interposed between cord 20 and the exterior beltsurface 13, and during processing a portion of the rubber extrudesthrough the interstices 33, 34 of the seamless tubular knit textilematerial 15, but preferably does not fully encapsulate all of the knitmaterial, leaving protruding yarn segments 36, 38, 40 on the exterior,as shown in FIG. 9. Alternatively, but less preferably, the knitexterior may bear a layer, preferably thin (for example of 0.002 inches(0.051 mm) to 0.020 inches (0.508 mm) thick, more preferably 0.003inches (0.076 mm) to 0.007 inches (0.178 mm) thick, with its ends buttspliced together), of rubber or other suitable friction-engineeredmaterial at the outer surface 13 of the belt.

[0036] The belt teeth 50 may, in customary fashion, carry an outerabrasion resistant toothed fabric layer 51 adhered to the rubber of theteeth. Typical suitable materials include a stretch nylon square wovenfabric material or knit material. The teeth 50 may also includetransverse stiffening elements or other reinforcements not shown.

[0037] A method of forming the belt of FIG. 2 will be discussed inrelation to the apparatus of FIG. 7. On to a building drum 31 is firstapplied, optionally, an elongated transfer label 51 upon which isimprinted any desired indicia, e.g. product numbers, trademarks, countryof origin, to be imparted to back surface 13 of the belt. This transferlabel typically is a relatively thin film of Mylar or other plasticmaterial bearing heat or pressure sensitive ink printing which duringvulcanization is transferred from the Mylar backing to the outer surface13 of the belt. As the belt is built inverted, the next layer applied onthe drum is the seamless tube 30 of knit textile material 13 of FIG. 8,which is expanded and elastically stretched sock-like over the mandrel31 and grips, without wrinkles, against the outer surface of drum 31with interposed transfer label 51. In this fashion, the wales 35 runlongitudinally of the drum, i.e. parallel to its axis. Although it hasbeen found satisfactory to employ a single tubular knit layer 30,obviously depending on the application, two or more layers couldadvantageously be used, with any intervening rubber layer applied asdictated by the application.

[0038] Over the seamless tubular knit 15 is wrapped one or more layersof elastomer such as adhesion gum rubber 17. Preferably the ends of thelayer(s) are butt spliced to avoid a lap which might otherwise bereflected as a protrusion or bump in the exterior surface 13 of thebelt. This gum layer 17 may alternatively be fiber loaded with anysuitable reinforcement fiber such as cotton, polyester or aramid, or mayitself include one or more textile reinforcing layers embedded therein.Onto gum layer 17 is applied, by helically winding, strain-resistingtensile cord 20 in typical fashion. The tensile cord may be closely orwidely spaced, as needed, and an appropriate amount of winding tensionis used, with the ends 20 a secured, as shown. Lastly, layer 24 whichwill serve as the undercord of the belt, is wrapped over the helicallywound cord 20. This material may be gum stock, or include discrete fiberloading 29 to enhance the modulus of the ribs 23, 25, 27, 29.

[0039] Once the sleeve has been built up on drum 31, the assembly may beplaced inside a vulcanizing bag with steam pressure introduced to pressthe bag radially inwardly against the outer surface of the sleeve(against layer 24), consolidating and vulcanizing the sleeve incustomary manner. The mold may then be disassembled and the sleevedemolded. The sleeve may then be placed on a grinding drum and theprofile of ribs 23, 25, 27, 29 formed with complimentary shaped grindingwheels or flycutters, removing undercord material between the ribs, andup to apices 26. Alternatively, the ribbed profile may be formed byusing a matrix airbag during vulcanization on drum 31, where the shapeof the airbag is impressed into the overcord section 24. Alternatively,an airbag can be placed over mandrel 24 and the sleeve pressed outwardlyduring vulcanization against a rigid outer shell member having theconjugate shape of ribs 23, 25, 27, 29 formed in the shell. Variousmethods of manufacture will be appreciated by those having skill in thisart.

[0040] Although the foregoing process has been described in relation tothe manufacture of a multi-V-ribbed belt, it will also be appreciated bythose skilled in the art that the synchronous belt of FIG. 6 can also beformed on an appropriate apparatus similar to FIG. 7. For instance, toform the belt of FIG. 6, the mandrel or drum 31 will typically havelongitudinally extending teeth on its surface which form belt teeth 50.In this manner, the belt will be built upright rather than inverted. Theradially outermost layer to be applied will be the seamless tubular knittextile material 15 in the form of tube 30 which has been radiallystretched or expanded, as shown in phantom in FIG. 8 to apply over thepartially formed belt sleeve. In that case, an outer airbag will be usedto press the rubber/composite materials radially inwardly against thetoothed mold mandrel 31.

[0041] With similar modifications the belt of FIG. 2 could also be builtupright, rather than inverted. In that case the outermost layer ispreferably the seamless knit tube, less preferably with a furtherexterior layer of gum rubber thereover, butt spliced to avoid laps.

[0042] Whether producing the belt of FIG. 2 or FIG. 6, by using theouter seamless tubular knit material 15 in accordance with theinvention, the standard transfer label 51 may be employed withoutproducing any, or any significant, discontinuities on the outer surface13 of the belt which would otherwise serve as noise generators whenimpacting backside idlers or tensioner or other pulleys. That is, whenthe tubular knit material is positioned at the exterior belt surface 13as shown in FIG. 9, with the outermost yarn fibers 36, 38, 40 being freefrom full encapsulation by the rubber matrix, when the transfer label 51is pressed against the outer surface 13 during vulcanization, as shownin FIG. 10, the printed material is transferred to the back of the beltwithout substantially affecting its flat, generally planer outersurface. This has unexpectedly been found to be the case even afterremoval of the Mylar printing strip. Thus, there are no ridges ordiscontinuities or steps impressed into the outer surface 13. This is incontrast with prior art belts shown in FIG. 11 using a calendared(frictioned) Bannered fabric 53, having an outer thin rubber layer 55 atthe exterior surface 13′ of the belt. In the case of the prior art belt,when the Mylar transfer label 51 is vulcanized into the outer surface ofthe belt, it presses against the rubber layer 55, causing it to compressand exude out the edges when the rubber is softened due to heat andpressure. When the Mylar strip is removed from the finished belt ridgesor depressions 57 are left behind on the exterior belt surface 13′.These ridges 57, which typically are at least about 0.0015 inches (0.04mm) higher than the depressed printed portion of the belt, create noisewhen impinging against idler and tensioner pulleys. In contrast, inpractice the height of the step formed by removal of the Mylartransparency in accordance with the subject invention is insubstantial(typically about 0.0008 inches (0.02 mm)) insofar as noise generation isconcerned.

EXAMPLES

[0043] Belts made in accordance with the invention of FIG. 2 and themethod described with regard to FIG. 7¹ generally ran quieter than theprior art belts of FIG. 11 on the test drive of FIG. 1, as measured bysensor 18. The prior art belts exhibited a noticeable thumping noise;the belts of the invention did not. The belts of the invention alsogenerally experienced less weight loss compared to FIG. 11 belts usingcalendared “Flex-weave” fabric (120° included angle, bias, Banneredfabric—registered trademark) or tire cord, as overcord reinforcement 53.

[0044] A comparison was also made between the belt of FIG. 2 of theinvention (using a 0.012 inch thick (0.305 mm) adhesion gum layer 17),and the same belt without layer 17. The belt of the invention with gumlayer 17 had a measured fabric to stock adhesion of 2.8 N/mm compared to0.9 N/mm for the belt omitting layer 17.

[0045] The belt and method of the invention offer a number of benefits.There is a complete elimination of overcord fabric splices, therebyproviding the most robust manufacturing process possible to assure theelimination of all lapped or splice caused noise. The knitted tubes ofthe invention offer 100% and more of stretch capability for the buildingprocess, limiting the number of knit tube sizes required to cover theproduct length ranges encountered, thereby limiting the number ofdifferent tube sizes required. Textile surfaces on the overcord offercertain coefficient of friction engineerability accomplished bycontrolling the amount of gum rubber strikethrough. Furthermore,Bannering, calendaring and jacket preparation are eliminated.

[0046] Although the present invention has been described in detail inthe foregoing for the purpose of illustration, it is to be understoodthat such detail is solely for that purpose and that variations can bemade therein by one skilled in the art without departing from the spiritor scope of the present invention except as it may be limited by theclaims. The invention illustratively disclosed herein may be suitablypracticed in the absence of any element which is not specificallydisclosed herein.

What is claimed is:
 1. A power transmission belt comprising a rubberbody, a strain-resisting tensile member embedded in the body, anovercord section terminating in a generally flat exterior belt backsurface, and an undercord section, the improvement comprising a seamlesstubular radially stretchable textile material positioned at the exteriorbelt back surface and a rubber layer adhered to the tubular textilematerial on its under-surface and interposed between the tubular textilematerial and the strain-resisting tensile member.
 2. The powertransmission belt of claim 1 wherein the tubular textile material is aseamless tubular knit material formed of yarns, fibers of whichpositioned at the exterior belt back surface are free from fullencapsulation in the rubber body.
 3. The power transmission belt ofclaim 1 wherein the tubular textile material is a circular jersey knit.4. The power transmission belt of claim 1 having on its exterior beltback surface a transfer label imprinted thereon, without significantnoise-generating steps in such surface.
 5. The power transmission beltof claim 1 wherein the seamless tubular radially stretchable textilematerial is fully encapsulated in rubber material.
 6. The powertransmission belt of claim 1 in the form of a multi-V-ribbed belt inwhich the ribs, located in the undercord, are loaded with discretereinforced fibers.
 7. The power transmission belt of claim 1 in the formof a synchronous belt having a plurality of teeth disposed on theunderside of the belt body adapted to mesh with the teeth of a sprocket.8. A method of producing a power transmission belt comprising: (a)forming a vulcanizable belt sleeve by: applying a seamless tubularradially stretchable textile material about the exterior surface of abelt building drum; wrapping a rubber layer serving as an adhesion gumlayer over the seamless tubular textile material; helically windingstrain-resisting tensile cord members about the rubber layer; applying afurther rubber layer over the exterior of the helically wound tensilecord; and (b) subjecting the belt sleeve to heat and pressure tovulcanize the same.
 9. The method of claim 8 including applying a filmtransfer label with indicia thereon, between the building drum and theseamless tubular radially stretchable textile material.
 10. The methodof claim 8 wherein the radially stretchable textile material is aseamless knit tube.